Such locks are of special interest for hotels, where it is not uncommon that the guests forget to leave the key upon departure or that the key is lost in some other way. For security reasons, it will be desirable to change the combination of the lock to a new key. Also a number of other institutions will have similar requirements.
Locks of this type are previously known for instance from U.S. Pat. Nos. 3,271,983 and 3,661,763. Here the blocking pins consist of rod magnets which are movably arranged between the key and code members. The blocking pins may be moved axially to releasing position by corresponding magnetized sections on the key and code members. Since in these locks the blocking pins may be moved only by means of magnetic forces which are relatively weak, dust and other foreign matter can reduce the movability of the blocking pins to such an extent that they can not be moved sufficiently by the magnetic sections on, for instance, the key member in order for the lock to be opened. This problem is aggravated by the fact that iron containing dust will be attracted by the magnetic blocking pins. In addition, there is the possibility of unintentional de- or re-magnetization of the key member so that it may no longer be used to open the lock. Furthermore, it is relatively costly to change the combination of the lock because the key and code members are relatively expensive to manufacture, due to the necessary magnetizing equipment. Finally these locks do not possess the desired resistance to picking.